The present invention relates generally to heat exchangers and more specifically to such heat exchangers having a pressure responsive by-pass assembly integral therewith.
Heat exchangers of the finned conduit type are employed for cooling or otherwise transferring heat between two fluids generally one of which is circulated internally through conduits provided in the heat exchanger core and the other being passed over the exterior of the conduits and associated heat radiating fins. Such heat exchangers are commonly employed in heavy construction machinery as well as other apparatus for use in cooling oil, hydraulic fluid or the like. In such applications the oil may have a relatively high viscosity when cool such as at startup of the equipment and become thinner as it is warmed during use. This high viscosity may cause higher than desired pressure in the inlet header of such oil coolers due to the viscous resistance of oil flow through the relatively small passages in the heat exchanger core. Further, the resistance may prevent a sufficient amount of oil from being circulated through the system which in an extreme case could result in excessive equipment wear. Accordingly, it is desirable to provide pressure responsive by-pass means to allow the high viscosity oil to by-pass the heat exchanger core. Such a by-pass means may also operate to prevent unnecessary cooling of the oil thereby assisting the apparatus in reaching a steady state operating temperature more rapidly. Such an arrangement offers a further advantage in that should the heat exchanger core passage become constricted or plugged due to contaminants in the oil or damage to the core portion, the pressure responsive by-pass means will operate to insure a sufficient fluid flow to prevent equipment damage due to lack of oil.
In one arrangement for supply such a by-pass arrangement of which applicant is aware, the heat exchanger is constructed with elongated inlet and outlet headers each havng a fitting provided thereon. A self-contained pressure relief valve is provided having one end threadedly installed in one of the fittings. Generally, a flexible host fitting is then threaded into the other end of the pressure relief valve to which a hose may be secured such as by means of a conventional strap clamp. A similar hose fitting may be threaded into the other header fitting and the other end of the hose secured thereto again by a conventional hose clamp.
While this arrangement provides an effective pressure relief by-pass means, it is relatively expensive to install in terms of both components and labor. Further, the need for the numerous fittings, each being interconnected increases the chances of leaks occurring such as by loosening of the fittings due to vibration or the like. Also, as the hose is generally of the rubber neoprene or other synthetic composition material, it is subject to degradation due to the elements as well as vibrational wear should it touch another surface during operation of the equipment. Thus, periodic inspections and/or replacements of these hoses is required.
Accordingly, the present invention provides an improved heat exchanger particularly suited for use as an oil cooler which has an integral pressure responsive by-pass assembly provided thereon. This by-pass assembly includes a continuous fluid conduit extending between and in fluid communication with the inlet and outlet headers. A pressure relief valve is removably installed within the conduit and operates to prevent fluid passage therethrough unless a predetermined pressure differential occurs between the two headers. Preferably, the one or more of openings provided in the headers which receive the end portions of the by-pass conduit are formed by tee drilling, which is a form of metal spinning so as to provide an outwardly projecting collar portion around the periphery of the opening. This collar operates to increase the surface area opposing the by-pass conduit sidewall thereby facilitating brazing of the joint therebetween and significantly reducing the possibility of leaks developing or other failures occurring. Additionally, in order to allow installation of the pressure relief valve subsequent to completion of the heat exchanger assembly operation, the fluid by-pass conduit may have one end extending through one of the headers and a suitable closure or plug member removably installed therein. This feature also enables rapid replacement of the pressure relief valve if necessary.
Additional features and advantages of the present invention will become apparent from the following description of the preferred embodiments taken in conjunction with the drawings and claims appended hereto.